Table 2.

Comparison of radiological findings in AIP, ARDS, HAPE, and COVID-19.

Disease	Radiological findings
AIP	Ground grass attenuation areas with a mosaic pattern and air space consolidation in dependent areas, bibasilar, diffuse or localized in the upper lobes. Intra-alveolar fibrosis with consolidation in the organizing phase with possible bronchiectasis formation and cyst, especially in the non-dependent lung areas. In “pulmonary” ARDS appearance is asymmetric, with a mix of consolidation and ground-glass opacification, possible pleural effusion, and emphysema. Predominance of air bronchograms and pneumomediastinum In “extrapulmonary” ARDS predominantly symmetric ground-glass opacification are present with possible pleural effusion and emphysema. Ground-glass opalization and consolidation are greater in the central third of the lung than in the sternal or vertebral third without significant craniocaudal predominance. Consolidation is mainly distributed in the middle and basal levels as well as the vertebral position.
ARDS	Heterogenous foci of consolidation, ground-glass opacities (with gravitational gradient), and crazy paving, with predominance in the posterior and basal areas. Possible air bronchograms and small pleural effusions. In the organizing and fibrotic phase, traction bronchiectasis and reticulation may develop (anterior predominance).
HAPE	Unilateral or Bilateral asymmetrical alveolo-interstitial opacities with relative sparing of the periphery and apices, usually marginated, with patchy distribution and initial confluence in the perihilar region, and prominent horizontal fissure, interlaced with normally aerated areas. Possible lobar consolidation limited by horizontal fissure. Focal patchy air-space opacities/ consolidations. Pulmonary edema usually occurs in areas of high blood flow, with a patchy distribution.
COVID-19	Phenotype 1 (or L) usually presents as multiple focal over perfused ground glass opacities and normally aerated areas and is prevalent of mild to moderate diseases. Possible diversion of ventilation toward non-dependent aerated lung regions and reduction in pulmonary perfusion due to increased airway pressure, collapse of capillaries and/or microthrombosis and formation of no recruitable atelectasis. Phenotype 2 (or H) shows a patchy ARDS-like pattern, with inhomogeneously distributed and hyper/hypo-perfused areas that is prevalent of severe disease. Increased lung weight and consolidated and non-aerated lung regions mainly distributed in the dependent lung regions. In these clinical conditions, areas with low V/Q persist but associated with areas of “true shunt”. Phenotype (F) which represents a final evolution to fibrosis.

Table Legend: AIP, acute interstitial pneumonia; ARDS, Acute Respiratory Distress Syndrome; COVID-19, Coronavirus disease 2019. HAPE, high-altitude pulmonary edema.